Google has announced the launch of mobile image ads as part of the company's growing wireless advertising initiative.

Google unveiled the ad units -- really just pint-sized banners -- on its mobile blog.

According to Google, the ads are targeted based on what users search for on their phones. Google said it will serve only one ad on a screen in deference to the limited amount of real estate available on mobile devices.

"For advertisers, mobile image ads serve as a branding tool and have shown to have good clickthrough rates," Alexandra Kenin, a product marketing manager for Google Mobile Ad, said in a blog post on the company's site.